1. Field of the Disclosure
The present disclosure generally relates to laboratory animal husbandry, bedding, and enrichment; particularly the automation and manufacture thereof; particularly for rodents.
2. Description of the Prior Art
Nesting material has been identified as the best ‘environmental enrichment’ for improving animal wellbeing, health, productivity, and scientific data quality in mice. Existing nesting enrichments are either easily dispensed, but are unsuitable for building nests (and are generally ignored by mice); or allow good nest-building, but are very difficult to handle and cannot be automatically dispensed. Given the need of automation in the industrial scale of mouse husbandry, current mouse enrichment is largely limited to nesting enrichments that mice don't use, or enrichments such as shelters which can be detrimental to mouse wellbeing.
The known environmental enrichments are additions to husbandry that allow animals to cope with stressors and challenges in the captive environment (Olsson & Dahlborn 2002; Garner 2005; Würbel & Garner 2007). As a result of reduced psychological and physiological stress, enrichments improve the wellbeing, comfort, health, and productivity, of animals; and in the case of lab animals, improve the quality and validity of data they yield. (Benaroya-Milshtein et al. 2004; Garner 2005; Benaroya-Milshtein et al. 2007; Würbel & Garner 2007). Accordingly enrichment is now generally required for laboratory animals in the US (Institute of Laboratory Animal Resources (ILAR) 2010).
In the case of mice, nesting material has emerged as the most effective enrichment in terms of mouse wellbeing (Olsson & Dahlborn 2002). Other enrichments, particularly shelters, are widely used (e.g. www.bio-serv.com). However shelters, in particular, often induce territoriality and aggression, and so can inadvertently introduce stress, impair wellbeing, and increase the variability of animals (Barnard et al, 1996; Olsson & Dahlborn 2002; Howerton et al. 2008). Shelters induce aggression in part because they are highly valued, so while they are of benefit to singly housed mice; they are a liability for group housed animals. However they are a specific case of a more general issue—which is that just because a cage looks enriched to humans, doesn't mean that it is to an animal. In fact the vast majority of commercially available mouse enrichments have never been studied scientifically to assess their efficacy or whether they might have unexpected consequences. Another excellent example can be found in mouse nesting enrichments. Until recently the predominant nesting enrichment was the ‘Nestlet’, a square of compressed cotton that can, in theory, be shredded by the mouse to make a nest. However mice often fail to make use of Nestlets; and in fact mice provided with Nestlets build no better nests than mice provided with an equal weight of additional bedding (Hess et al. 2008).
Mice in the wild build nests by weaving fibrous materials (such as grass, or straw) into a compact and rigid scaffolding, to hold layers of insulating softer materials. Mice process nesting materials extensively to generate the properties required. Thus, when preparing ‘scaffolding’ materials they chew along the material fraying out individual fibers to aid adhesion when the materials are eventually woven together. Similarly, they chew and fray insulating and lining materials into an expanded ‘fluff’ (Van Oortmerssen 1971; Latham & Mason 2004). Thus while Nestlets may provide a suitable material for these inner layers, they are useless without a suitable structural material. Accordingly, when Nestlets are compared against a shredded paper product that does allow the construction of a ‘scaffolding’ mice build far better nests with this alternative material (‘Eco-bedding’, www.fibercorelle.com) (Hess et al. 2008). Furthermore, when provided with a mix of Eco-bedding and tissue paper, mice use the Ecobedding to build a scaffold, and line the nest with tissue paper (Hess et al. 2008).
Nests probably benefit mice in captivity for two reasons. First, like shelters, they probably serve a psychological function as a place of refuge from the perceived threats of predation inherent in the close interaction of mice with their human caretakers. Second, work in our lab has shown that mice are cold stressed under normal laboratory conditions, that mice adjust nest structure to ambient temperature (building better nests in colder temperatures), that nests (built with Eco-bedding) reduce radiative heat loss by about 5° C., and that feed conversion (the weight of food eaten per g of body weight gained) is reduced up to 5-fold (unpublished data, and: Gaskill et al. 2009a; Gaskill et al. 2009b). Thus mice without nests are metabolically, physiologically, and behaviorally abnormal—with consequences (aside from the massive increase in food consumption) including effects on body composition, growth and reproduction, and metabolically dependent processes such as pharmacodynamics. Aside from the obvious scientific benefits, food is one of the major costs in mouse housing.
However, the complex nature of nest-building behavior, and the complex mixture of materials it requires, presents three key challenges to providing nesting material which have limited its adoption in the industry:
a) Identifying a material that mice can and will use effectively to build nests;
b) Ease of handling, standardization of the amount of material provided, and automation of cage provisioning; and
c) Unintended negative consequences, particularly poor ammonia control, and difficulties in cage cleaning.
Existing materials represent a poor trade-off between these concerns. As outlined above, Nestlets, are standardized and easily handled, but are a very poor nest-building material, and are often ignored by mice. Eco-bedding, allows mice to build excellent nests, but is hard to handle and standardize (it is typically loose-packed in bulk and must be measured and dispensed by hand), and can present difficulties in cage cleaning (particularly because it can clog older vacuum systems used in large facilities). Mice can build surprisingly good nests with pine shavings, given enough time to process the material, but pine shavings are a notoriously poor choice for ammonia control. In fact, driven largely by concerns over ammonia control, the industry is generally moving towards bedding materials that provide less thermal and physical comfort (such as corn-cob), further magnifying the need for a suitable nesting enrichment.
Cage cleaning problems are limited to well-understood defects in vacuum system design (e.g. narrow tube diameter, tight tube corners, and long tube runs), are readily solved, and are not addressed here[j1]. Ideal materials have already been identified—namely long shredded paper strips, potentially combined with other softer materials such as facial tissue paper (referred to as ‘tissue paper’ herein).
There is therefore an unsatisfied need for the handling, standardization and dispensing of nesting material on an industrial scale.